The word also shows up in news reports about Malaysian Airlines Flight 370:

“For 16 long days, Sarah Bajc was the face of determined hope,” a Washington Post reporter wrote about the American schoolteacher whose boyfriend, Philip Wood, is among the missing.

Bajc, despite the overwhelming odds, believed her boyfriend was alive. She continues to give interviews and maintains a Facebook page and a Twitter account devoted to learning the fate of the missing jetliner.

All this talk of hope made me wonder about the role it plays in our live.

It was a surprise to learn that hope is the focus of research in fields as varied as psychology, theology, nursing, medicine, philosophy and psychoneuroimmunology.

It’s the subject of dozens of books with titles like The Anatomy of Hope, Hope in the Age of Anxiety and Making Hope Happen. It’s even been quantified, as one researcher has measured the contribution of hope to productivity and academic achievement (14 and 12 percent, if you’re wondering).

Hope differs from optimism — you can be a pessimist, in fact, and have hope. And hope is grounded in more practicality and action than simply wishing. It also has a strong link with faith, or at least a basic belief in the goodness of humanity.

“Hope is both the earliest and the most indispensable virtue inherent in the state of being alive.” — Erik Erikson

We develop hope early. “Hope, inculcated in our lives from our earliest childhood experiences … is as natural to us as water is to fish,” says Nancy Snow, professor of philosophy at Marquette University who’s writing a book called The Landscape of Hope, an overview on the subject.

Hope, for many, may be based in faith. “There’s a very strong spiritual foundation to hope,” says Carol J. Farran, professor and alumni association endowed chair of health and aging at Rush University and a co-author of Hope and Hopelessness.

The Bible mentions “hope” more than 180 times, according to Anthony Scioli and Henry B. Biller, authors of Hope in the Age of Anxiety.

Hope has been found to give us an evolutionary advantage. “Hope is a game-changer,” Snow says, because it gives us the motivation to try to change our circumstances. “It gives us strength to get through really difficult times.”

Stories abound of those who manage to survive harsh circumstances because of hope.

“If we lose our hope, that’s our real disaster.” — Dalai Lama

Farran, who works with caregivers of Alzheimer's patients says: “The person who is hopeless doesn’t have the strength to move forward." She believes we may have to consciously work at developing and maintaining hope, and that it’s possible for hope — and hopelessness — to co-exist as we switch back and forth between those emotions.

Hope affects our reaction to serious illness. Snow points out the case of a woman she knew who was diagnosed with pancreatic cancer and told there was a 5 percent survival rate.

“How do I know I’m not in that 5 percent?” the woman asked.

“There is an authentic biology of hope,” writes Dr. Jerome Groopman in his book, The Anatomy of Hope. “Belief and expectation — the key elements of hope — can block pain by releasing the brain’s endorphins and enkephalins, mimicking the effects of morphine.”

Groopman acknowledges that much of the popular literature on the curative effects of hope is “vague, unsubstantiated, merely wishful thinking.”

But personal experience taught him the power of hope. As Groopman writes in his book, he ruptured a lumbar disc in 1979 when training for the Boston Marathon. Six months later, he had a spinal fusion that failed. His surgeon said there was no hope, and for 19 years, Groopman lived “in a labyrinth of relapsing pain and debility.”

Not until another surgeon offered hope and a plan that worked did Groopman’s pain subside.